The present invention relates to a thin-film magnetic head for writing and reading, the head having a layer-wise buildup on a nonmagnetic substrate and being used with a recording medium provided with a magnetizable storage layer, into which information can be written along a track by vertical magnetization. Such magnetic heads have a ring-head-like conducting body for carrying the magnetic flux, with two magnet legs, of which the poles facing the recording medium are arranged one behind the other as seen in the direction of motion of the head and have a predetermined spacing from each other, and which delineate a space in between, through which the turns of an at least largely flat coil winding extend. Such a magnetic head is shown, for instance, in European Patent Application EP No. 0 012 910 Al.
The principle of perpendicular magnetization for storing information is generally known (see, for instance, "IEEE Transactions on Magnetics, " vol. MAG-16, no. 1, January 1980, pages 71 to 76; DE-OS No. 29 24 013 or the above mentioned European Patent Application). For this principle, which is often also called vertical magnetization, special recording media in the form of rigid magnetic storage discs, flexible individual discs (floppy discs) or magnetic tapes are required. A corresponding recording medium has at least one magnetizable storage layer of predetermined thickness which contains a magnetically anisotropic material, especially of a CoCr alloy. The axis of the so-called easy magnetization of this layer is oriented perpendicularly to the surface of the medium. By means of a separate magnetic head, the individual sections of information are then written-in along a track as bits in successive sections, also called cells or blocks, by suitable magnetization of the storage layer. In practice, the magnetic flux changes, i.e., the transitions from one direction of magnetization to the opposite one, are used as the information. The bits so obtained have a predetermined extent, also called wavelength, in the longitudinal direction of the track. This dimension can be substantially smaller than the limit which is given by the demagnetization with the method of longitudinal (horizontal) storage. Thus, the information density in the recording medium can advantageously be increased by the principle of vertical magnetization.
The write and read heads known for the principle of longitudinal magnetization, i.e., heads with which the write as well as the read function can be executed, however, cannot be used directly also for vertical magnetization. If these heads, which generally have a ring head-like shape, are used, a conduction of the flux in a circuit closed as far as possible with low magnetic resistance can be achieved also with a flux conduction according to the desired principle of vertical magnetization. However, it is difficult to generate a sufficiently strong writing field in the case of high bit density and an accordingly small gap width of the ring head.
One is therefore compelled to develop special write and read heads for the principle of vertical magnetization. A design of a magnetic head suitable for this purpose comprises, in general, a so-called main pole by which a sufficiently strong vertical magnetic field for reversing the magnetization of the individual sections of the storage layer is generated. A necessary magnetic return can then be achieved, for instance, by means of a so-called auxiliary pole which is located, for instance, on the same side as the main pole (see, for instance, "IEEE Trans. Magn.", vol. MAG-17, no. 6, November 1981, pages 3120 to 3122, or vol. MAG-18, no. 6, November 1982, pages 1158 to 1163; "J. Appl. Phys.", vol. 53, no. 3, 1982, pages 2593 to 2595; DE-OS No. 29 24 013 or the above cited European application).
In this type of magnetic head which is known, for instance, from the above mentioned European Patent Application, the auxiliary pole is to serve in any case only for the return of the magnetic flux. While possible concurrent writing of this pole can be tolerated if necessary if the writing main pole lags behind it and can therefore overwrite information written by the auxiliary pole, the so-called air gap formed between the two poles would have to be relatively wide in order to at least largely suppress concurrent reading of the auxiliary pole with its trailing edge, in order to ensure a far-reaching reduction of the magnetic flux density at the auxiliary pole. Gap layers correspondingly wide are difficult to realize, however, for magnetic heads to be made with a thin-film technique. In addition, the read signal obtainable with magnetic heads of this type is generally relatively weak since in this type, the read as well as the write function must be executed with only a single coil winding.
Because of these difficulties, magnetic heads have also been proposed, in which the use of a special auxiliary pole is dispensed with ("IEEE Trans. Magn.", vol. MAG-18, no. 6, November 1982, pages 1170 to 1172; European Patent Application 0 071 489 A2). For this type of magnetic head, only a single magnet leg is provided which faces the recording medium and with which a planar write and read coil winding is associated. The necessary magnetic return is then accomplished by the stray flux. With such a magnetic head, also called a single-pole head, a sufficiently distinct high-frequency write signal can be generated if the inductivity of the coil winding is not too large. On the other hand, no sufficiently large read signal can be obtained if the auxiliary pole is omitted.
Due to these mentioned problems in reading, systems are also known in which the write and read function can be executed by respective separate heads. These heads can then be adapted better to the respective function (see, for instance, "IEEE Trans. Magn.", vol. MAG-16, no. 5, September 1980, pages 967 to 972). Accordingly, ring heads known per se are used for reading, while the writing must be performed by the mentioned single-pole heads. A known write head suitable for this purpose comprises on its side facing the storage layer of the recording medium, a main pole of a longitudinal extent of, for instance, 3 .mu.m, opposite which is located on the back of the recording medium a substantially large auxiliary pole. The second ring head required only for reading, on the other hand, has a gap width of, for instance, 0.2 .mu.m (see "IEEE Trans. Magn.", vol. MAG-17, no. 6, November 1981, pages 2538 to 2540). Such systems for the magnetic reading and writing with special heads adapted to the respective function, however, are relatively expensive from a design point of view.